The reinforcing armature or reinforcement of the tires, and notably of motorcycle tires, is at the present time, and more often than not, formed by stacking one or more plies, conventionally designated “carcass plies”, “breaker strips”, etc. This manner of designating the reinforcing armatures originates from the manufacturing process, consisting in producing a series of semi-finished products in the form of plies, provided with filament reinforcements, often longitudinal, which are thereafter assembled or stacked in order to form a tire blank. The plies are produced flat, with large dimensions, and are then cut according to the dimensions of a given product. The plies are also assembled, initially, substantially flat. The duly produced blank is then shaped to adopt the toroidal profile typical of tires. The so-called “finishing” semi-finished products are then applied to the blank, to obtain a product ready for vulcanization.
Such a “conventional” type method involves, in particular for the tire blank manufacturing phase, the use of an anchoring element (usually a bead wire), used to provide the anchorage or to secure the carcass armature in the area of the beads of the tire. Thus, for this type of method, a portion of all the plies forming the carcass armature (or of just some) is turned up around a bead wire arranged in the bead of the tire. In this way, an anchorage is created for the carcass armature in the bead.
The generalization in the industry of this type of conventional method, despite numerous variants in how to produce the plies and the assemblies, has led those skilled in the art to use a vocabulary modeled on the method; hence the generally accepted terminology, notably comprising the terms “plies”, “carcass”, “bead wire”, “conformation” to designate the transition from a flat profile to a toroidal profile, etc.
There are now tires that do not strictly speaking comprise “plies” or “bead wires” according to the above definitions. For example, the document EP 0 582 196 describes tires manufactured without the use of semi-finished products in the form of plies. For example, the reinforcing elements of the different reinforcing structures are applied directly to the adjacent layers of rubbery mixtures, the whole being applied in successive layers to a toroidal core, the shape of which is used to directly obtain a profile matching the final profile of the tire during manufacture. Thus, in this case, the terms “semi-finished”, “plies”, and “bead wire” no longer apply. The basic products such as the rubbery mixtures and the reinforcing elements in the form of threads or filaments, are applied directly to the core. Since this core is toroidal in shape, it is no longer necessary to form the blank to change from a flat profile to a torus-shaped profile.
Moreover, the tires described in this document do not have the “conventional” carcass ply turn-up about a bead wire. This type of anchorage is replaced by an arrangement wherein circumferential threads are arranged adjacent to said sidewall reinforcing structure, the whole being embedded in an anchoring or linking rubbery mixture.
There are also methods of assembly on toroidal core that use semi-finished products that are specially adapted for rapid, effective and simple placement on a central core. Finally, it is also possible to use a mix comprising both certain semi-finished products to produce certain architectural aspects (such as plies, bead wires, etc.), whereas others are produced from the direct application of reinforcing mixtures and/or elements.
In the present document, in order to take account of the recent technological developments both in the manufacturing field and in product design, the conventional terms such as “plies”, “bead wires”, etc., are advantageously replaced by terms that are neutral or independent of the type of method used. Thus, the term “carcass-type reinforcement” or “sidewall reinforcement” is valid for designating the reinforcing elements of a carcass ply in the conventional method, and the corresponding reinforcing elements, generally applied at the sidewall level, of a tire produced according to a method without semi-finished products. The term “anchorage area”, for its part, may designate either the “conventional” carcass ply turn-up about a bead wire of a conventional method, and the assembly formed by the circumferential reinforcing elements, the rubbery mixture and the adjacent sidewall reinforcement portions of a bottom area produced using a method with application to a toroidal core.
As in the case of all the other tires, there is a trend towards the radialization of tires for motorbikes, the architecture of such tires comprising a carcass armature formed by one or two plies of reinforcing elements forming with the circumferential direction an angle that can be between 65° and 90°, said carcass armature being radially topped by a crown armature formed at least by generally fabric reinforcing elements. However, there are still non-radial tires to which the invention also relates. The invention further relates to partially radial tires, that is to say tires whose reinforcing elements of the carcass armature are radial over at least a part of said carcass armature, for example in the part corresponding to the crown of the tire.
Many crown armature architectures have been proposed, depending on whether the tire will be intended for mounting at the front of the motorbike or for mounting at the rear. A first structure consists, for said crown armature, in employing only circumferential cables, and said structure is more particularly employed for the rear position. A second structure, directly inspired by the structures commonly employed in tires for private passenger vehicles, has been used to improve the resistance to wear, and consists in the use of at least two breaker strips of reinforcing elements parallel to one another in each ply but crossed from one ply to the next by forming with the circumferential direction acute angles, such tires being more particularly suited for the front of the motorbikes. Said two breaker strips can be radially topped by at least one ply of circumferential elements, generally obtained by helically winding a strip of at least one rubber-coated reinforcing element. The patent FR 2 561 588 thus describes such a crown armature, with at least one ply whose reinforcing elements form with the circumferential direction an angle that can vary between 0° and 8°, the modulus of elasticity of such elements being as high as at least 6000 N/mm2, and, arranged between the carcass armature and the ply of circumferential elements, a damping layer mainly formed by two plies of elements crossed from one ply to the next, forming between them angles of between 60° and 90°, said crossed plies being formed by fabric reinforcing elements having a modulus of elasticity of at least 6000 N/mm2.
The document EP 0 456 933, in order to confer on a motorbike tire excellent stability at high speed and an excellent ground contact property, teaches, for example, forming a crown armature with at least two plies: a first ply, radially closest to the carcass armature, consisting of ropes oriented with an angle of between 40° and 90° in relation to the circumferential direction and the second ply, radially closest to the tire tread, consisting of ropes helically wound in the circumferential direction.
The U.S. Pat. No. 5,301,730, with a view to enhancing the driveability of a tire for the rear position of a motorbike, proposes a crown armature consisting, from the radial carcass armature to the tire tread, of at least one ply of substantially circumferential elements and two plies of elements crossed from one ply to the next, forming with the circumferential direction an angle that can be between 35° and 55°, the ply of elements which are parallel to the circumferential direction being able to be formed by elements made of aromatic polyamide, and the plies of crossed elements of aliphatic polyamide.
The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.
A circumferential plane or cross-sectional circumferential plane is a plane perpendicular to the axis of rotation of the tire. The equatorial plane is the circumferential plane passing through the centre or crown of the tire tread.
A radial plane or mid-plane is a plane that contains the axis of rotation of the tire.
The axis of rotation of the tire is the axis about which it revolves in normal use.
The transversal or axial direction of the tire is parallel to the axis of rotation of the tire.